Oil wells typically require some servicing during the lifetime of the wellbore whether it be to increase production, such as by acidizing or fracturing the formation and the like, perform testing on the formation or the wellbore integrity, replace components such as sucker rods or production tubing or casing or to perform a variety of other operations as necessary.
Service rigs are typically designed to at least have the capacity to trip out or run in the production tubing and to run in and trip out a variety of downhole tools. Conventionally, the service rig generally comprises at least a drawworks for raising and lowering tubulars and the like and typically a sandline for raising and lowering downhole tools such as during swabbing operations. Each of the drawworks and sandline are typically powered by diesel motors to which they are mechanically connected. The conventional powering systems typically do not provide as fine a motor control of the drawworks and the sandline as is desired for servicing operations. AC motors are used in the drilling industry where weight is less of a limitation on design.
Production tubing typically cannot handle as much torque as a drill stem and therefore more control is required for tripping out and running in of production tubing as compared to drill pipe. Conventional positioning of components into or out of the wellbore for servicing therefore has required careful and continuous monitoring and management of at least the drawworks and sandline systems by the onsite driller to ensure safe operations.
Conventionally power has been provided for braking systems on the drawworks and the sandline drums through diesel motors and mechanical connections associated therewith. Similarly in conventional rigs, hydraulic motor systems are also provided to operate tongs and slips required to break or make sections of tubing from the tubing string as it removed from or inserted into the wellbore.
In many cases, where the formation is to be treated by chemicals, pumping units are brought onsite to provide specialized treatment fluids which are pumped into the wellbore. The pumping unit is typically provided with a separate power source onsite.
Service rigs are generally portable rigs which comprise a transportable platform mounted on an undercarriage and which are powered by a propulsion system for moving the rig from wellsite to wellsite. Conventionally propulsion systems for service rigs are separately powered and typically comprise at least a large diesel engine carried on the platform and mechanically connected to the transmission through a gear box. A plurality of axle/wheel configurations are typically available for the undercarriage so as to conform to Department of Transport regulations. Service rigs must be capable of carrying a significant amount of weight given the diverse equipment mounted thereon and must also be able to meet regulations governed by road bans to permit servicing of wellbores throughout the year and under a variety of environmental condition. This becomes a challenge for rig manufacturers who must balance the competing requirement of the industry for greater functionality of the rig while trying to reduce the weight to meet the road ban conditions.
Additionally, there are electrical requirements onsite to support servicing operations such as hotel loads, onsite lighting and other such requirements which are conventionally provided by one or more small generators separately provided.
There is a need to provide improved power systems for service rigs that are efficient, supply the needs of the operations at the wellsite and which do not add significantly to the problems associated with the weight of the rig so as to maintain maximum transportability.